Field of Invention
The present invention relates to a lock-up device, particularly to a lock-up device for a torque converter for transmitting a torque from an engine to a transmission-side member and absorbing and attenuating torsional vibration.
Background Information
Torque converters are often equipped with a lock-up device for directly transmitting a torque from a front cover to a turbine. As described in Japan Laid-open Patent Application publication No. 2002-089657, a lock-up device of this type includes a piston capable of being frictionally coupled to the front cover, a drive plate fixed to the piston, a driven plate, a plurality of torsion springs and an intermediate member. The driven plate is fixed to the turbine of the torque converter, and is elastically coupled to the drive plate in a rotational direction through the plural torsion springs.
In the device, the piston is mounted between the front cover and the turbine, and the torque of the front cover is configured to be transmitted to the lock-up device when an annular friction member fixed to the outer peripheral part of the piston is pressed onto a friction surface of the front cover. Accordingly, the torque is transmitted from the lock-up device to the turbine. At this time, variation in torque inputted from an engine is absorbed and attenuated by the plural torsion springs of the lock-up device.